This invention relates generally to shrouded bellows and, more particularly, to modeling techniques used to predict natural frequency responses in tube systems that include shrouded bellows.
Shrouded bellows or sealed ball joints are often used in gas turbine engine ducting systems to connect adjacent sections of fluid carrying tubing which require articulation therebetween. The shrouded bellows provide a flexible joint that prevents leakage of the fluid flowing therethrough despite potential movement between the adjacent sections of tubing. Such movement can be for example, caused as a result of thermal growth in the ducting system during engine operation.
Shrouded bellows are typically located in various locations within and around the engine. To design shrouded bellows and associated hardware to withstand High Cycle Fatigue (HCF) stresses, modeling techniques are used to predict natural frequency responses in the ducting systems including the shrouded bellows components. Known modeling techniques use analytical models that approximate shrouded bellows natural frequency response with manufacturer-supplied test data. Such test data is typically obtained from static stiffness component testing. The analytical models incorporate static stiffness data by assigning a spring constant to various spring elements used to represent the shrouded bellows within the analytical models. The spring elements provide the bellows stiffness input for an analytical determination of the system natural frequency response. Because the shrouded bellows natural frequency response is based on static stiffness test data, the ability of the analytical models to accurately estimate the natural frequency response of shrouded bellows is potentially limited.